Polyamide resins have conventionally been used in industrial fields of automotive components, mechanical components, electrics/electronics components, by virtue of their excellent mechanical strength and heat resistance. In particular for applications to electrics/electronics components, required level of flame resistance has been elevated, even escalated up to a level of flame resistance higher than the self-extinction performance inherent to the polyamide resins. For this reason, investigations have extensively been made on elevation of flame resistance level, and more specifically on materials satisfying the level V-0 specified by UL94 by Underwriters Laboratories. In particular, as for compositions mixed with a high concentration of glass fiber, there have been growing demands on development using a non-halogen-type flame retarder, following the trend of time. In these applications, also demands on the tracking resistance, represented by IEC Standards in Europe, have been becoming more and more stringent.
Patent Document 1 discloses a polyamide resin composition composed of melamine cyanurate and/or its derivative, and an inorganic filler, excellent in mechamical characteristics, thermal characteristics and flame resistance. The level of flame resistance is, however, V-2 specified by UL 94, while giving no disclosure on resin compositions having flame resistance of higher levels, more specifically, the level V-1 or higher.
Patent Document 2 is an invention which relates to a flame retarder combination containing a component, as a first component, which contains phosphinate salt represented by a specific structure and/or a diphosphinate salt represented by a specific structure and/or a polymer of these species; and a second component which contains a condensed product of melamine and/or a reaction product of melamine with phosphoric acid and/or a reaction product of a condensed product of melamine with phosphoric acid and/or a mixture of these species. The Patent Document 2 describes also a method of using the flame retarder combination for the purpose of turning thermoplastic resins into flame retardant resins. In Example, there is exemplified a polyamide resin composition satisfying flame resistance of the level V-0 specified by UL94 ( 1/16 inches thick), obtained by mixing a reinforced polyamide resin containing 30% of glass fiber, with a flame retarder combination composed of a phosphinate salt (first component) and melamine polyphosphate (second component).
The polyamide resin composition exemplified in Example is, however, discussed only for its data on flame resistance, while giving no description on any other characteristics including mechanical characteristics and electrical characteristics.
Patent Document 3 discloses a flame-retardant polyamide resin composition containing the flame retarder combination (containing 1 to 30% by weight of each of the first component and the second component) disclosed in Patent Document 2; and 5 to 40% by weight of an inorganic filler (glass fiber, wollastonite, talc, calcined kaolin, mica, etc.). In Examples, there is described that polyamide resin compositions containing 20% by weight and 30% by weight of glass fiber exhibit excellent flame resistance and tracking resistance. The resin composition may, however, be degraded in the mechanical strength by mixing of the flame retarder. No description is given on the sectional geometry of the glass fiber.
Patent Document 4 discloses a flame-retardant aromatic polyamide resin composition obtained by mixing (a) 100 parts by weight of aromatic polyamide resin, (b) 0.1 to 100 parts by weight of crosslinked phosphazene compound, (c) 1 to 60 parts by weight of inorganic fibrous material, and (d) 1 to 60 parts by weight of magnesium hydroxide. Claim 1 of Patent Document 4 specifies the amount of mixing of the (c) inorganic fibrous material as 1 to 60 parts by weight relative to 100 parts by weight of the (a) aromatic polyamide resin, but the amount of mixing of the (c) component described in Example is only as much as 7 parts by weight or around, showing no specific examples relevant to mixing at high concentrations.
There is no description also on exemplary cases of using a glass fiber as the (c) component. Example shows data on the flame resistance, but shows no data on the mechanical strength. The resin composition manufactured by adopting the technique disclosed in Patent Document 4 may sometimes be degraded in the mechanical strength, providing difficulty in reconciling flame resistance and mechanical strength even if the technique is adopted.
Patent Document 5 describes that, by using the glass fiber having a flattened cross-sectional geometry, instead of glass fiber which is a representative reinforcing fiber, the glass fiber is increased in the specific surface area from the cross-sectioned glass fiber having the circular, thereby the adhesive effect with a matrix resin composition increases, and describes also that the mechanical strength may be improved, by elongating the length of fiber in a molded article (average fiber length is 0.57 mm for a cocoon-like sectional geometry, in contrast to 0.47 mm for a circular sectional geometry). Patent Document 5, however, exemplifies only the cases applied to PBT resin, AS resin and ABS resin. These resin compositions might be effective in improvement in the tensile strength and surface smoothness, and in prevention of warping as compared with a circular cross-sectioned glass fiber, but the impact strength thereof is almost equivalent to the impact strength of a resin composition using a circular cross-sectioned glass fiber particularly when a polyamide resin is used as the thermoplastic resin, and the impact strength thereof is insufficient for practical molded articles use. There is no description on specific examples of mixing of a flame retarder, nor description on correlation of the cross-sectional geometry of glass fiber and the flame resistance.
Patent Document 6 discloses a flame-retardant polyester resin composition composed of (A) a crystalline thermoplastic polyester resin, (B) 1 to 60% by weight (in composition) of glass fiber having a flattened sectional geometry characterized by a ratio of the major axis of a section perpendicular to the longitudinal direction (longest straight distance of the section) to the minor axis (longest straight distance in the direction perpendicular to the major axis) of 1.5 to 5, (C) 0.5 to 25% by weight (in composition) of a halogen-containing organic flame retarder, and (D) 0.1 to 20% by weight (in composition) of an inorganic flame retardant additive. The technique, however, adopts the (C) halogen-containing organic flame retarder, wherein addition of the flame retarder may be causative of degradation in the mechanical strength such as impact resistance, or production of a hydrogen halide gas in the process of combustion, raising problems of pollution of mold, and failure in obtaining a molded article of good appearance. Moreover, Patent Document 6 gives no description still also on correlation between the sectional geometry of glass fiber and flame resistance.    Patent Document 1: Japanese Laid-Open Patent Publication No. S54-16565    Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-72978    Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-292755    Patent Document 4: Japanese Laid-Open Patent Publication No. 2001-131409    Patent Document 5: Japanese Laid-Open Patent Publication No. S62-268612    Patent Document 6: Japanese Examined Patent Publication No. H7-21105